davis



Sept. 11, 1951 A. R. DAVIS 23,409

TRANSFORMER Original Filed Nov. 24, 1941 4 SheetS -Sheec 1 &

INVEMTOR.

BY ri/mz z $4 4105 W K A. R. DAVIS Sept- 11, 1951 TRANSFORMER 4Sheets-Sheet 2 Original Filed Nov. 24, 1941' INVENTOR. 1 flea-2 15?0414.5

v, 6 w M r 7 A P 11, 1951 A. R. DAVIS Re. 23,409

TRANSFORMER Original Filed Nov. 24, 1941 4 Sheets-Sheet 5 &

fij) INVENTOR. 142/54 flQV/S 147'7'0/P/VEY Sept. 11, 1951 A. R. DAVISTRANSFORMER Original Filed Nov. 24, 1941 i 4 SheetsSheet 4 v uvwszvroa140/54 53 iii AS 6 7" TOFA EY Reissued Sept. 11, 1951 rial No. 420,286,November. 24, 1941. Application for reissue March 2 6, 1951, Serial No.

Matter enclosed In heavy brackets appears in the": original intent butforms no this reissue specification; matter printed in italics indicatesthe additions made by reissue. I

My invention relates to an improved method of controlling lights, orelectrical apparatus of any type requiring a variable A. C. voltage onsingle or multiple circuits.

A further object is to provide a device that can be adjusted to anypoint within the range of the device from above the full line voltage tozero on single or multiple circuits.

A still further object is to provide a new transformer and brushcombination which through the use of various simple improvementsprevents the usual internal losses and heating of windings due to theshort circuiting of adjacent turns by the usual type of brush, making atransformer of high efliciency which will last longer and give greatersatisfaction without any of the usual troubles in operation andmaintenance.

A still further object is to provide a [dinner] dimmer for multiplecircuits which is controlled by finger operated sliders so arranged thatthey may be worked individually or in unison as the time andcircumstance require.

The essential feature of the invention is an electrical control devicefor raising and lowering the voltage through a continuous range withoutcircuit interruption on single or multiple circuits. The principle bywhich the continuous voltage is maintained is that there are twocontactors on each brush insulated from each other and arranged in sucha position and mechanically connected togetherin such a manner that theycontact one turn or two adjacent turns of the transformer winding at alltimes. In other words this is an auto transformer designed for use tocontrol electrical circuits by raising or lowering voltage to any givenload suchas a. motor, bank of lights, electric furnace, andthe like.

With this device there is no short circuiting between the turns of themain transformer windings when'a brush is overlapping any two adjacentturns. When the brush is overlapping two adjacent turns the difi'erencein potential is corrected by connecting one side of the brush with oneend of a single turn of wire wound on the core and wound in the samedirection as the winding of the particular brush contacts. The other endof this single turn is connected to one lead of the primary winding ofan auxiliary tramformer. The other end of the primary winding is thenconnected back to the other side of the brush. In the secondary windingof this auxiliary transformer there is a resistance in series with thewinding. It is this combination of devices that prevents any shortcircuiting in the main winding. For each separate circuit there hasto'be a separate brush with its own separate turn and auxiliarytransformer. It is this improved relationship of devices that makes itpossible to use a multiple numberof sliders on a single winding and yethave no short circuiting of the winding, for each circuit takes care ofits own local exciting current.

The winding of the transformer can be or the auto-transformer type. orwith a primary and secondary winding. These windings are'made in such amanner that the brush can contact each individual turn used in thevoltage regulation by passing over it. Where a primaryand secondarywinding is used, the secondary winding may be extra heavy, and of fewturns where a heavy current is to be regulated with only a small rangein the voltage. The auto-transformer type of winding in most cases isthe desired type of winding because of simplicity and lower cost ofmanufacture, etc. a

The shape of the core would determine too.

great extent the general shape of'the I and the building or an eiilcienttransiormenk The three" eneral shapes of cores used ,for

transformers are the jcorepshell, and toroidal,

Where circular motion-is desired, a when coil may be used with 'a singlebrush of the aforementioned ype on an arm and .revolved about the axisof the toroid.. The shell typeof transformer may be employed in mydevice where both a primary and secondary winding are used with thbrushes, making contact with the sec ondary. p 1

For easy and-eilective operation when more than one winding is used forthesliders to contact; it is desirable to-have all the sliders at oneend or the' transformer whentheyfare at full voltage, andthe other endwhen at no'voltage'. In order to do this thewindingsare wound with acorrect polarity in the manner they will be connected together, whichwould be in either series or parallel, for single phase currents; andeither delta or star, for three phase currents.

It is often desirable to raise the voltage above the line voltage. To dothis. extra turns are put on each leg above where the line voltage isapplied. The number of extra turns will raise the voltage in directratio to the number of turns on the rest of the connected coil.

These objects I accomplish with the device illustrated in theaccompanying drawings in which similarnumerals and letters of referenceindicate like parts throughout the several views and as described in thespecification forming a part of this application and pointed out in theappended claims.

In the drawings in which I have shown my device,

Figure 1 is a plan view of the transformer.

Figure 2 is a side elevation of Figure 1.

Figure 3 is an end view of Figure 1.

Figure 4 is a diagrammatic view of the wiring system used in thetransformer.

Figure 5 is a section of line 5-5 of Figure 8.

Figure 6 is an enlarged end view of one of the brushes.

Figure '7 is a diagrammatic showing of the contacts of a brush engagingthe windings of the transformer.

Figure 8 shows the next advanced position of the brush from that shownin Figure '7.

Figure 9 shows the brush in its next relative position.

Figure 10 shows the last position of the brush before again entering theposition shown in Figure 7.

Figure llis a diagrammatic showing of a modification of the inventionmodified to show a toroidal transformer.

This invention primarily would be used for stage lighting installationsto control the various lights on the stage border and other pointsdesired, but is just as important and pertinent to other types ofvoltage regulating transformers for industrial uses.

The transformer is made of a rectangular core A, having two legs 5 and Iaround whichthe windings B and C are wound. The windings B and C arecontinued toward one end of the transformer core beyond the point wherethe lines I and 8 are tapped onto the windings, providing extra windingswhich are utilized so that brushes do not come to rest on a blank space,but provides extra windings which may be utilized when required tocorrect line voltage drop by stepping up the voltage above the operatingvoltage of the line.

-The finger control brushes are made of two contact strips 9 and Illspaced apart by insulation [4] 32. The two brushes are connected to andlongitudinally operated along the slider and current carrying bus barsII and I2. One of these bars II is connected to the load L, shown as aseries of globes and thence through the common ground wire I! to thealternator [G] E.

The transformer is made with an elevated non-conductor block 23 at eachend thereof in which the ends of the two bus bars H and I! are supportedand carried and springs 2! are mounted on the top bar II to limit theendward movement of the brushes so that they will always be on thewindings of the transformer and will never pass to far over the ends ofthe windings of the transformer.

The brushes are all alike, so I will describe but one. Each brushconsists of a main body block 25 of non-conducting material, and thisblock is bored transversely to receive the bus bars II and I! to permitthe brush to be moved longitudinally along said bars. The top of eachbrush is flat and carries a vertical strip 28 secured therein bysuitable locking bars 21; On the top end of the strip I provide a fingercontact block II secured in a like manner to the strip. This thin stripis made to allow a cover to be placed over the entire transformer ifdesired, and at the same time permit the finger operation of the brusheswithout any danger of the operator getting a shock through carelessness.Each of the holes vertical slot 34 of block 25. Each leg of the brush isprovided with an insulation base 35 to insure that no bending orbreaking of the brush will engage the surface of the winding of thetransformer and cause a short circuit. The depending ends 36 of thebrushes [engages] engage the surface of the winding B or C. The width ofthe depending ends 36 [being] are such that neither one will be as greatas the width of the insulation between the winding of the transformer.

and the width of the two are so spaced that one will always make contactwith a turn of the winding. Tension springs 31 are set in sockets in theblock 25 and press down upon the top side of each leg 3| of the brushesto insure an even pressure on the winding of the transformer. A flexiblelead 38 is secured to the leg 30 of the brush ill on one end andthe-other end connected to the plate 40 on the end of sleeve 29. The leg,3. of the brush 9 is connected to a plate II on the end of the othersleeve 28 by the flexible lead 42. The plate 4| is made with a hole lltherethrough around the bar I! to insure that there will be not shortcircuiting of the two slider bars II and I2. As shown in Figure 1, thereare a multiplicity of these bus bars and an equal number of fingercontrolled brushes and their relative positions shown in Figure 1 showthe positions of any given four of these brushes and illustrates thatany position desired for any given circuit may be obtained without[effecting] a!- jectinq any of the other circuits, each being utilizedas an independent dimmer although they all operate on the sametransformer.

The auxiliary transformer T is shown as a primary winding ii, asecondary winding l1 and.

a resistance R. connected with the secondary winding. The bar ii isconnected to one end of a single turn winding l8 wound around the end ofthe core A, in the same direction a the winding which the brushcontacts, and thence out to the primary winding [5 of the auxiliarytransformer T to the circuit. The auxiliary transformer T is wound withthe correct number of turns so that it will limit the current, when thesingle turn is short circuited, to a small value. but when the full loadcurrent is passing through it, the reactance is very small, having noap- 'preciable effect on the load. The value of the resistance R isadjusted to give the minimum loss when the maximum load current ispassing through the transformer T, which loss is a very small value. Itwill be obvious that for each slider or brush and circuit connectedthereto there must be a separate single turn it and an auxiliarytransformer T.

In the diagrammatic view shown in Figure 4, I have shown four differentindividual brushes with four individual loads L, with each brushprovided with its individual single turn it and the correspondingindividual auxiliary transformer T. These brushes are also set to showthe cycle of operation of a single brush as it passes through from oneturn to the next of the windings, however, to show this more clearlyFigures 7, 8, ii and 10 show the relative positions of a brush as itpasses across the length of the transformer windings. In order to getthe proper position for the relative advancement of a single brush.these brushes shown in Figure 4 are not shown spaced the same distanceapart. as in this type of showing it is necessary to show the contactsin such relative positions as they will make when in actual operationover the surface of the transformer windings.

Figures 7 to 10 inclusively show the relative positions a single brushwill have to the windings of the transformer, and these positions arealso the positions shown in Figure 4 for the four brushes shown therein.

In position 1 shown in Figure 'l, the brush is shown with one side orcontact 8 engaging one winding of the transformer, while the other sideor contact I is over an insulated area. In this position the currentpasses through the brush 8, through the bar H to the load L. As thebrush advances to the position shown as position 2 of Figure 4 or inFigure 8, the contact Ill engages an advanced winding of the transformerwhile the contact 9 is still on the first winding, thus two windings arecontacted at the same time by the two side contacts 9 and Hi. Thedifference in potential is equalized in this position by the single turnit, which is wound in the same direction as the winding on which thebrush is contacting; the transformer T having no effect upon thecircuit. Approximately half-of the load or current passing through eachside of the brush and out to the load L, shown as the series of globesIll. As the brush advances to its next position 3, shown in Figure 9,the contact II is still contacting the same turn of the winding whilethe contact 9 is now over an insulated area. In this position thecontact lli carries the current through the bar I! to the single turnl8, through the transformer T, back to the bar II and out to the load L.In this position the reactance in the transformer T is very small,

} so that the current passes readily to the load L.

As the brush advances to position 4 of Figure 10, both of the contacts9, and I0 ride on a single winding of the transformer causing a shortcircuit in the single turn I8. The current passes through both contacts,the one side going directly to the load, the other through the singleturn, the transformer T, and out to the load. The transformer limits theshort circuiting current to a small value and dissipates it as heatthrough the resistance R, utilizing the effect of the auxiliarytransformer T and the single turn it to the fullest extent, keeping allheating out of the winding of the transformer. This cycle is completedand repeated through each successive movement of the brushes over eachsuccessive turn.

The single turn winding connected between the contactors 9, 10,heretofore termed "contacts,

impresses a voltage on the contactors equal and opposite to the voltageof the main winding spanned by the brush when the contactors are eachcontacting the tap of a separate winding at the same time. In Fig. 1 thecontactor 10 engages the tap of the windin having the lower voltage andcontactor 9 engages the tap' of the winding having the higher voltage.Thus, on

spanning windings contactor 9 is at a higher voltage than contactor 10.The contactor 10 is connected to the low voltage end of the single turnwinding 18 and contactor 9 is connected to the high voltage end of thesingle turn winding 18. The winding 18 thu impresses a generated voltageon the brush opposing the voltage difierence between the spannedwindings and equalizing this voltage difference and eliminating thecurrent that would normally circulate through a shorted winding. Theauxiliary current limiting transformer T is preferably connected betweenthe load current carrying bus bar 11 connected to contactor 9 and thehigh voltage end of the single turn winding 18 so that the load currenton passing through the contactor is shunted around the transformer T.

A carbon brush or other type of brush having high resistance may be usedinstead of brush shown in Figures 5 and J to limit the current whenpassing from one winding to the other,eliminating the use of the smalltransformers and the single turn on a multiple slider installation wherethe device is only to be used for dimmers for lighting circuits withmultiple finger control; but such use causes a heating efl'ect in thewindings of the transformer, which is an undesirable feature as is wellknown in the art.

A choke coil or coils could be used in place of the single turn ortransformers, but with a multiple number of sliders, the heating effectin the main winding would become larger and larger when two or moresliders engage the same turn of the winding. This is mentioned so thatfor some installation, if required by specifications, such aninstallation may be made without departing from the principle of themultiple brush contacts on a single transformer winding and individualfinger control of any circuit.

It will be obvious that various modifications and variations may be madein the structure of the device without departing from the spirit of theinvention or the scope of the claims.

The operation of the device is obvious from the above description.

Having thus described my invention, I desire to secure by Letters Patentand claim:

1. A transformer comprising a core; a main winding on said core; amultiplicity of independently operated, individual circuit load controlbrushes mounted to operate longitudinally along the surface of said mainwinding, making continuous contact therewith; a multiplicity of singlewindings each being of the same potential as one complete turn of themain winding, each being connected in series with an auxiliary currentlimiting transformer and connected to one of the individual controlbrushes so that the single winding is either in parallel with the turnsof the main winding when the brush is covering adjacent turns, that arebeing traversed, or forms a closed circuit within itself at such timesas any brush is completely contacting a single turn of the main winding,said auxiliary transformer limiting the current in the single winding.

2. A transformer comprising a core, a main winding on said core, amultiplicity of independently operated, individual circuit load controlbrushes mounted to operate longitudinally along the surface of said mainwinding, making continuous contact therewith, a multiplicity of singlewindings each being of the same potential as one complete turn of themain winding and opposing said potential, each being connected in serieswith an auxiliary current limiting transformer aspen and connected toone of the individual control brushes so that the single winding iseither in parallel with the turns of the main winding when the brush iscovering adfacent turns and in this position tends to equalize thepotential between the turns that are being traversed, or forms a closedcircuit within itself at such times as anil brush is completelycontacting a single turn of the main winding, said auxiliary transformerlimiting the current in the single winding.

3. A transformer comprising a core, a main winding on said core having aplurality of turns developing a magnetic flit: on energization and withtaps in predetermined uniform spacing along said winding for the tappingof voltages therefrom, a brush assembly movable along said winding andengaging'said taps, said assembly having two contactors spaced apartfrom each other along the line of movement of said assembly developing avoltage difference between them and having an over-all width andseparation to span said taps with one contactor in engagement with onetap and the other contactor in engagement 8 with another tap and also inanother position to engage the same tap simultaneously by bothcontactors, a local circuit connected between said contactors andcomprising an auxiliary winding coupled with a magnetic flux creating avoltage between said contactors opposite to the voltage between saidtaps to tend to equalwe the diflerence in potential between thecontactors in said position spanning said contacts and a currentlimiting means in series with said auxiliary winding in said localcircuit acting to limit the short circuit current within said'localcircuit to a small value when said contactors are in engagement with asingle tap, each ofsaid contactors having an individual width less thanthe separation of said taps so that as one contactor is moved to anintermediate position on one tap the other contactor is positioned inthespace between said contacts and the current passes readily through saidcontacting contactor to the load.

. 1 ARIEL R. DAVIS.

'No references cited.

